How to append all elements of one list to another one?

Question

Probably a simple question but I would like to parse the elements of one list individually to another. For example:

a=[5, 'str1'] 
b=[8, 'str2', a]

Currently

b=[8, 'str2', [5, 'str1']]

However I would like to be b=[8, 'str2', 5, 'str1']

and doing b=[8, 'str2', *a] doesn't work either.

score 28 · Answer 1 · edited Aug 03 '17 at 12:10

28

Use extend()

b.extend(a)
[8, 'str2', 5, 'str1']

edited Aug 03 '17 at 12:10

answered Aug 03 '17 at 12:09

akash karothiya

score 18 · Accepted Answer · answered Aug 03 '17 at 12:10

18

You could use addition:

>>> a=[5, 'str1']
>>> b=[8, 'str2'] + a
>>> b
[8, 'str2', 5, 'str1']

answered Aug 03 '17 at 12:10

fredtantini

score 12 · Answer 3 · answered Aug 03 '17 at 12:12

12

The efficient way to do this is with extend() method of list class. It takes an iteratable as an argument and appends its elements into the list.

b.extend(a)

Other approach which creates a new list in the memory is using + operator.

b = b + a

answered Aug 03 '17 at 12:12

abhinav

score 3 · Answer 4 · answered Aug 03 '17 at 12:11

3

>>> a
[5, 'str1']
>>> b=[8, 'str2'] + a
>>> b
[8, 'str2', 5, 'str1']
>>>

for extend() you need to define b and a individually...

then b.extend(a) will work

answered Aug 03 '17 at 12:11

score 0 · Answer 5 · answered Aug 03 '17 at 12:10

You can use slicing to unpack a list inside another list at an arbitrary position:

>>> a=[5, 'str1'] 
>>> b=[8, 'str2'] 
>>> b[2:2] = a   # inserts and unpacks `a` at position 2 (the end of b)
>>> b
[8, 'str2', 5, 'str1']

Similarly you could also insert it at another position:

>>> a=[5, 'str1'] 
>>> b=[8, 'str2'] 
>>> b[1:1] = a
>>> b
[8, 5, 'str1', 'str2']

5 Answers5